Hydrogels are among the most exploited materials in several applications, including tissue engineering, drug delivery, surgical adhesives and 3D bioprinting. There is growing interest in injectable hydrogels, especially as applied to surgical adhesives and bioprinting materials. Current methods for the in situ irreversible formation of hydrogels include chemical reactions, reversible polymer-particle interactions and physical associations, such as in the case of thermosensitive sol-gel reversible hydrogels. Methods of flow induced gelation have been previously reported, and they include flow induced gelation of micellar solutions, vortex induced gelation of protein solutions, and shear induced gelation of polymer-clay suspensions.
Meanwhile, microfibers are widely exploited in biomedical applications. A relevant feature of microfibers is that compounds, such as drugs, droplets, and biological materials, e.g., cells, can be readily encapsulated in their structure. Microfluidics provides the possibility to encapsulate compounds and manipulate the physical properties of a single fiber, such as Young modulus, aspect ratio (L/D, where L is length and D is the diameter of a fiber) and morphology. The microfibers can be dispersed in a liquid medium thus creating a suspension. Fiber suspensions are usually observed to behave as shear thinning fluids, i.e. the suspension viscosity decreases upon the action of flow, even when changing fiber size, aspect ratio, flexibility, or in the presence of noticeable normal stress differences. Shear thickening, where the viscosity increases with increasing shear rate, is rarely observed in flowing fiber suspensions, however it can be indicative of a gelation process. For example, shear thickening is observed with some polymer-particle suspensions, where the mechanism of gelation involves the bridging of particles with polymer chains. Another flow-induced gelling system is the flow-induced irreversible formation of nanogels from worm-like micelle solutions, which involves the rearrangement of the micelle structures to form junctions and branches that result in an entangled network. However, there are currently no processes or products that produce hydrogels in situ from flow induced gelation of microfibers, nor are there presently any products that use microfibers to form hydrogel materials.
Improved hydrogels and methods for producing hydrogels, beyond the synthetic and physical approaches that are currently available, would provide for new and emerging applications and would be a welcome addition to the art.